The invention relates to the detection of environmental alpha particle radiation and, more particularly, a novel miniature detector of radon and thoron gas concentrations for personal or area use.
Radon gas is a decay product of the element radium-226 which is found in soils and rocks which can diffuse through physical cracks and soil pores and enter the breathable atmosphere. Structures such as homes and other buildings can trap the radon gas inside them because of typically low air ventilation rates. Concentrations of radon gas as a result can rise to high concentrations which adversely affect the health of people who come in contact therewith.
In general, continuous radon detection instrumentation is costly, large and requires electric power. Such detection equipment is also known to often require operation by highly skilled technicians, and is generally used for research purposes. As a result, integrating radon monitors have been developed in the art, as disclosed in U.S. Pat. No. 4,800,272 (Harley et al.), U.S. Pat. No. 5,068,538 (Harley) and U.S. Pat. No. 5,134,297 (Harleyet al.), all of which have common inventorship and assignee as the present application and are incorporated herein by reference.
Thoron (radon-220) is a decay product of the elements thorium and radium-224. Environmental cleanup or removal of radium and thorium, which are the sources of the two radioactive isotopes of radon, is often performed in the art. A high concentration of thoron which can be detrimental to the health of the people who come in contact therewith. It has not yet been feasible in the art to undertake large-scale radon and thoron measurement programs to determine the actual effects of different environmental levels of radon and thoron exposure in private residences and commercial buildings on a particular person or particular group of people. Furthermore, it is very difficult to measure thoron gas because it has a very short half life (txc2xd=55 seconds). There is thus a general need in the art for a compact, low cost and portable radon and thoron detector for personal or area use. Because of the presence of the two radioactive isotopes of radon, there is a need in the art for a method and apparatus of accurate personal exposure assessment with respect to hazardous concentration levels.
The present invention relates to a Rn222 (radon) and Rn220 (thoron) radiation monitor that uses alpha-track detection film in multiple, separate chambers to detect radiation. The invention further describes use of different diffusion barriers in each of the chambers to allow for signal differentiation between the chambers. The signal differentiation allows for differentiation between the levels of thoron and radon in the atmosphere tested.
In a preferred embodiment of the invention, the radiation monitor has three or four separate chambers, each with an electrically conductive housing and a cap with at least one opening to permit entry of ambient air. Inside each of the housings is an alpha-track detecting film, such as a solid-state nuclear track detector (SSNTD), with a thin electrically conducting cover. In one or more of the chambers is a diffusion barrier and seal placed within the housing to generally isolate the detecting film from thoron radiation in the housing. Use of diffusion barriers with different diffusion rates or properties allows for signal differentiation so that a specific measurement can be made of thoron levels separate from the radon levels present in the atmosphere tested.
In particular, the radiation monitor according to a specific embodiment of the invention comprises a first chamber, a second chamber and a third chamber. The first chamber comprises an electrically conductive housing having walls defining an internal volume of space, and at least one hole (or a plurality of holes) through a cap of the housing for permitting entry of ambient air into the internal volume of space. The first chamber further includes a solid state nuclear track detector (SSNTD) disposed within the housing with a thin electrically conducting cover. The second chamber comprises an electrically conductive housing having walls defining an internal volume of space, and at least one hole (or a plurality of holes) through a cap of the housing for permitting entry of ambient air into the internal volume of space. The second chamber further comprises a solid state nuclear track detector (SSNTD) disposed within the housing with a thin electrically conducting cover, and a diffusion barrier within the housing where the solid state nuclear track detector (SSNTD) is generally isolated from thoron radiation in the internal volume of space. The third chamber comprises an electrically conductive housing having walls defining an internal volume of space, and at least one hole (or a plurality of holes) through a cap of the housing for permitting entry of ambient air into the internal volume of space. The third chamber further comprises a solid state nuclear track detector (SSNTD) disposed within the housing with a thin electrically conducting cover, and a diffusion barrier within the housing, where the solid state nuclear track detector (SSNTD) is generally isolated from thoron radiation in the internal volume of space.
The radiation monitor according to yet another embodiment of the invention comprises four chambers, namely a first chamber, a second chamber, a third chamber and a fourth chamber arranged in a four-lobe manner. The four-chamber embodiment of the radiation monitor according to the invention advantageously achieves a more accurate radiation measurement because of the two pairs of chambers allow for measurement data comparison and data uncertainty calculations. The first pair of chambers includes one chamber without diffusion barriers and another chamber with a diffusion barrier. The second pair of chambers similarly includes one chamber without diffusion barriers and another chamber with a diffusion barrier.
In particular, in the four-chamber embodiment of the radiation monitor according to the invention, the first chamber comprises an electrically conductive housing having walls defining an internal volume of space, and at least one hole (or a plurality of holes) through a cap of the housing for permitting entry of ambient air into the internal volume of space. The first chamber further includes a solid state nuclear track detector (SSNTD) disposed within the housing with a thin electrically conducting cover. The second chamber comprises an electrically conductive housing having walls defining an internal volume of space, and at least one hole (or a plurality of holes) through a cap of the housing for permitting entry of ambient air into the internal volume of space. The second chamber further comprises a solid state nuclear track detector (SSNTD) disposed within the housing with a thin electrically conducting cover, and a diffusion barrier within the housing, where the solid state nuclear track detector (SSNTD) is generally isolated from thoron radiation in the internal volume of space.
In the second pair of chambers of the four-chamber embodiment of the radiation monitor according to the invention, the third chamber comprises an electrically conductive housing having walls defining an internal volume of space, and at least one hole (or a plurality of holes) through a cap of the housing for permitting entry of ambient air into the internal volume of space. The third chamber further includes a solid state nuclear track detector (SSNTD) disposed within the housing with a thin electrically conducting cover. The fourth chamber comprises an electrically conductive housing having walls defining an internal volume of space, and at least one hole (or a plurality of holes) through a cap of the housing for permitting entry of ambient air into the internal volume of space. The fourth chamber further comprises a solid state nuclear track detector (SSNTD) disposed within the housing with a thin electrically conducting cover, and a diffusion barrier within the housing, where the solid state nuclear track detector (SSNTD) is generally isolated from thoron radiation in the internal volume of space.